The Physics Applets for Drawing (PADs) allow students to interactively make graphs and other physics diagrams on the Web and have them evaluated. PADs are able to evaluate qualitative as well as quantitative drawings and to give customized feedback. These features greatly expand the range of exercises possible in a web-based homework system and make the latter more able to support research-based curricula. While feedback is an important component in learning, it is a challenge to provide enough feedback so that students do not become stuck and frustrated while at the same time not so much that it enables students to avoid thinking, particularly in an on-line environment. In this paper six different approaches to computer-based feedback are discussed along with how PADs could be used for different approaches. Participants are invited to discuss and make suggestions as to how PADs could be best used to support research-based curricula.